Multilayered printed board structure

ABSTRACT

A metallic printed board is formed by laminating an insulation layer on the surface of a metallic sheet as a base, and then electronic parts are mounted on the conductor pattern formed on the surface of the insulation layer. A double-sided printed board mounted thereon electronic parts is placed in parallel. Both the printed boards are supported and fixed monolithically by filling the space between the printed boards with an insulation resin and curing the resin. Furthermore, an insulation resin is laminated on the surface of the printed board in such a manner that the resin may cover the mounted electronic parts, and cured. The heat generated from the electronic parts can be efficiently transmitted to the insulation resins by using a resin having a high thermal conductivity for both of the insulation resins, and the heat is then emitted from the surfaces of the metallic sheet or the insulation resin.

BACKGROUND OF THE INVENTION

The present invention relates to a multilayered metallic printed boardfor mounting electronic parts such as resistors, capacitors, and ICchips at a high density, and to a molded module fabricated by joining amultilayer-type package obtained by forming the multilayered metallicprinted board into a box-shape etc., with a printed board provided as amother board, and then monolithically molding the joint structure usingan insulation resin.

Known printed boards devised for achieving a higher mount density ofelectronic parts include a metallic printed board comprising a metallicbase provided with two or more types of insulation layers thereon andfurther with a conductor pattern formed on the layers, and athree-dimensionally shaped metallic printed board obtained by subjectingthe metallic printed board to a bending or drawing process.

For instance, an Unexamined Japanese Patent Publication No. Hei-4-332188discloses the above described metallic printed board having a highermount density, which comprises insulation layers each differing fromeach other according to the characteristics of the electric circuitsmounted thereon.

However, the maximum mount density achieved so far is not alwayssufficiently high, because the maximum density for mounting theelectronic parts has been limited in the prior art metallic printedboards since the parts are mounted on a single plane.

Moreover, the insulation layers of the metallic printed boards have beenformed on copper foils or metallic boards by first applying a polyamicacid varnish as a precursor for a thermoplastic polyimide or athermoplastic polyimide varnish, either by a casting process or coatingprocess, and then adhering the foils or the boards together with orwithout. incorporating an insulation sheet between them. Such a processfor fabricating metallic printed boards requires special skill andcomplicated process steps.

In case of mounting the parts after subjecting the metallic printedboards to bending and drawing processes, the mounting operation has tobe applied to relatively deep portions. This makes surface mountingdifficult; hence, the process yields poor productivity and is thereforenot suitable for mounting irregularly shaped parts at a high density.

Furthermore, in case of applying the drawing step, the insulation layerin the corner portions also undergoes drawing. The depth of drawing istherefore limited because if the drawing is too deep, the insulationlayer is destroied. Thus, it has been found impossible to form thickmetallic printed boards, and hence, parts can not be formed in amultilayered structure. Accordingly, such a process has been foundunsuitable for increasing the mounting density.

In case an electronic part such as an IC which undergoes switchingoperation at high speed is directly mounted on a metallic printed boardhaving a thin insulation layer, it may malfunction due to the crosstalkwithin the electronic circuit or due to the exterior noise because ofthe high static capacitance of the insulation layer. Thus, theinsulation layer is preferably formed as thick as possible. On the otherhand, the structure of a package formed by subjecting a metallic printedboard to a bending or drawing process requires that the heat generatedby the electronic parts inside the structure is discharged asefficiently as possible to minimize the heat loss. In case of furthermounting bare chips inside the package, it is also desired to assure theprotection of the electronic parts against corrosion by environment andthe like.

In addition, it is not always easy to join the package to a mother boardat high precision and by a simple process. Moreover, the joint thusobtained after joining the package to the mother board has been found tobe insufficiently reliable due to the physical properties of thematerial.

SUMMARY OF THE INVENTION

The present invention has been accomplished to overcome theaforementioned problems. An object of the present invention is,accordingly, to provide a multilayered metallic printed board and amolded module which can be easily fabricated with high productivity andcan mount various types of parts at high density, and which are highlyreliable both in electric and mechanical properties.

The aforementioned object has been accomplished by a multilayeredmetallic printed board according to the present invention, whichcomprises a metallic printed board formed by laminating an insulatinglayer on a metallic sheet as a base and having electronic parts mountedthereon, and one or more printed boards each having electronic partsthereon and being laminated over the part-mounted side of the metallicprinted board, the space between the boards being filled with aninsulation resin.

Further, a molded module according to the present invention comprises aprinted board as a mother board having electronic parts mounted thereonand a multilayered package formed by folding an outer edge of themultilayered metallic printed board and filling the inside thereof withan insulation resin. The entire structure is formed monolithically byjoining the printed board as the mother board with the multilayeredpackage, and then filling around the joinded portion and the spacebetween the printed board as the mother board and the multilayeredpackage with an insulation resin.

According to the multilayered metallic printed board of the presentinvention, the electronic parts can be mounted on a plurality of layersto increase the mount density of the parts, and the heat radiated fromeach of the parts can be efficiently discharged via the insulation resinlayer and the metallic sheet.

According to the molded module of the present invention, the electronicparts are mounted on each of the printed board as a mother board, themetallic printed board of the multilayered package joined with themother board, and the printed board inside the package. Thus, the partsconstitute a layered structure to increase the mount density of theparts in the molded module which is formed of the integration of each ofthe boards. Further, the periphery of each of the mounted parts can befilled with the insulation resin and sealed in this manner. Thus, theheat generated from each of these parts can be efficiently dischargedvia the insulation resin, the metallic printed boards, etc., while eachof the parts are protected from the outer moisture and variousatmospheres.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a multilayered metallic printedboard according to a first embodiment of the present invention,

FIG. 2 is a cross sectional view showing a multilayered metallic printedboard according to a second embodiment of the present invention,

FIG. 3 is a cross sectional view showing a multilayered metallic printedboard according to a third embodiment of the present invention,

FIG. 4(a) is a cross sectional view showing a multilayered metallicprinted board according to a fourth embodiment of the present invention,

FIG. 4(b) is a view taken along the arrow in FIG. 4(a),

FIG. 5 is a cross sectional view showing a multilayered metallic printedboard according to a fifth embodiment of the present invention,

FIG. 6 is a cross sectional view showing a multilayered metallic printedboard according to a sixth embodiment of the present invention,

FIG. 7 is a cross sectional view showing a multilayered metallic printedboard according to a seventh embodiment of the present invention,

FIG. 8 is a cross sectional view showing a multilayered metallic printedboard according to an eighth embodiment of the present invention,

FIG. 9 is a cross sectional view showing a molded module according to aninth embodiment of the present invention,

FIGS. 10(a) and 10(b) are cross sectional views showing a metallicprinted board used in a tenth embodiment of the present invention,respectively,

FIGS. 11(a) to 11(e) are cross sectional views showing steps ofproducing a multilayered package used in an eleventh embodiment of thepresent invention, and

FIGS. 12(a) and 12(b) are cross sectional views showing a twelfthembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail below referring to the attached drawings.

FIG. 1 is a cross sectional view showing a multilayered metallic printedboard according to a first embodiment of the present invention.

In FIG. 1, a metallic printed board 1 is formed of a metallic sheet 2 asa base and an insulation layer 3 laminated on the upper surface of themetallic sheet 2. Although not shown in the drawing; conductor patternsare provided on the upper surface of the insulation layer 3 andelectronic parts 7 are mounted thereon.

A double-sided printed board 4 is disposed over the metallic printedboard 1 in parallel. Although not shown in the drawing, conductorpatterns are provided on both surfaces of the board 4 and electronicparts 7 are mounted thereon.

The space between the metallic printed board 1 and the double-sidedprinted board 4 is filled with an insulation resin 5. The insulationresin is cured to support and monolithically fix both the boards.

An insulation resin 6 is further laminated on the upper surface of thedouble-sided printed board 4 in such a manner that it may cover themounted electronic parts 7.

In this embodiment, the double-sided printed board 4 is placed over themetallic printed board 1 and arranged in parallel with it. As a result,the electronic parts are mounted on three layers to increase the mountdensity of the parts. On the other hand, the amount of heat generationper unit area due to the presence of the electronic parts 7 alsoincreases with the elevation of the mount density. However, since theinsulation resins 5 and 6 are placed in the periphery of the electronicparts 7, the heat thus generated can be efficiently transferred andabsorbed by the insulation resins 5 and 6, and then dischargedefficiently to the outside from the surface of the lower metallic sheet2 or the surface of the upper insulation resin 6. Thus, the temperatureof the electronic parts 7 can be maintained at a constant level orlower.

The insulation resins 5 and 6 may differ from each other in thermalconductivity, but preferably, they are resins having high values ofthermal conductivity.

The printed board laminated over the metallic printed board 1 may be asingle sided board, or may be a laminate of two or more boards.

FIG. 2 is a cross sectional view showing a multilayered metallic printedboard according to a second embodiment of the present invention.

This embodiment is characterized in a metallic printed board, and theother portions are the same as in the structure shown in FIG. 1.Accordingly, the common parts are indicated with the same symbols usedin FIG. 1 to refer to them without explanation. In FIG. 2, a metallicprinted board 11 comprises a metallic sheet 12 as a base. The uppersurface of the metallic sheet 12 is separated into two portions, and twoinsulation layers 8 and 9 differing from each other in physicalproperties are laminated on the two portions. The insulation layers 8and 9 have, though not shown in the drawing, a conductor pattern andelectronic parts 7, respectively.

If, for example, a power transistor, a rectifier diode, or any otherelectronic part which generate heat in large quantity is mounted on theinsulation layer 8, a material having a high thermal conductivity mustbe used as the insulation layer 8 to prevent the electronic part frombeing over heated.

If, for instance, an electronic part which undergoes a high speedswitching operation is mounted on the insulation layer 9, a materialhaving a low dielectric constant must be used as the insulation layer 9to lower crosstalk in the electronic circuit and to reduce the influenceto other circuits even at the generation of a switching noise.

In this embodiment, the insulation layer constituting the board isdivided into a plurality of sections, and each of the divided insulationlayers is made of a material having the optimal physical properties forthe electronic part to be mounted thereon according to thecharacteristics and the operational conditions of the parts. In thismanner, the parts can be mounted without influencing each other even incase of increasing the mount density. Thus, the circuit operation can bekept in normal condition while increasing the mount density of theparts.

In the previous embodiment, the insulation layers 8 and 9 were providedby dividing the metallic printed board 11 into two sections. However,the insulation layer can be divided into larger number of sections touse a plurality of insulation layers each differing in characteristics.Furthermore, a double-sided printed board 4 laminated over the metallicprinted board 11 can be divided into a plurality of sections to provideinsulation layers each differing in physical properties.

FIG. 3 is a cross sectional view showing a multilayered metallic printedboard according to a third embodiment of the present invention.

This embodiment is essentially the same as that illustrated in FIG. 1,except for a part of the double-sided printed board 4 and the insulationresins 5 and 6 shown in FIG. 1. The other parts are the same as those inFIG. 1, and are therefore indicated with the same symbols to makereference thereto without any explanation.

FIG. 3 shows a state in which there is a need to connect conductorpatterns, not shown in the drawing, of the respective metallic printedboard i and the double-sided printed board 4. In this state, a throughhole 27 penetrating an insulation resin layer 6, the double-sidedprinted board 4, and another insulation layer 5 is formed to connect theconductor patterns. The circuits on both of the laminated boards 1 and 4can be easily connected with each other by using the through hole 27.

The embodiment is also applicable to the foregoing first and secondembodiments.

FIGS. 4(a) and 4(b) are cross sectional views showing a multilayeredmetallic printed board according to a fourth embodiment of the presentinvention, wherein FIG. 4(a) is a cross sectional view and FIG. 4(b) isa view taken along line A--A in FIG. 4(a).

This embodiment is obtained by partly changing the double-sided printedboard 4 and the insulation layer 5 in FIG. 1. The other portions are incommon with those shown in FIG. 1. Accordingly, the common portions areindicated with the same symbols used in FIG. 1 to refer thereto withoutgiving any explanation.

In FIGS. 4(a) and 4(b), when there is a need that conductor patterns,not shown in the drawing, of a metallic printed board 1 and adouble-sided printed board 34 are to be connected with each other, theportion in the board 34 corresponding to the position of connection iscut out to fit and fix therein a through-hole substrate 36 shaped in thesame shape as that of the cut-out portion. The substrate 36 has such athickness that the lower end thereof is in contact with the board 1 whenlaminated, and a through hole 37 is formed therein along the thicknessdirection of the substrate.

Similarly, an electrode pattern 39 to be connected with the end of theouter periphery of an electrode pattern 38 is formed on the metallicprinted board 1 to be brought into contact with the end of the outerperiphery of the electrode pattern 38, and on the upper surface of thedouble-sided printed board 34. Thus, in the assembly, the board 34having the through hole substrate 36 fitted therein is mounted on theboard 1, and the electrode pattern 38 is connected by soldering with theelectrode pattern 39 formed on the upper surfaces of each of the boards1 and 34. Then, the boards 1 and 34 are fixed by filling the spacebetween the boards with an insulation resin 35, and by curing the thusfilled insulation resin. An insulation resin 6 is laminated on the uppersurface of the board 34 and cured in the same manner.

In this embodiment, the space between the metallic printed board 1 andthe double-sided printed board 34 is supported by the through-holesubstrate 36, and the electrode patterns 38 and 39 are soldered toattain mechanical stability between both of the laminated boards 1 and34. Similarly, the electrode patterns 38 and 39 are electricallyconnected to facilitate the circuit connection between the boards 1 and34.

Three or more through-hole substrates 36 can be incorporated in thestructure. Furthermore, the shape and the size of the through-holesubstrate 36 can be varied depending on the electronic parts 7 to bemounted, and on the constitution of the circuit.

The present embodiment is also applicable to any of the foregoing firstssecond, and third embodiments.

FIG. 5 is a cross sectional view showing a multilayered metallic printedboard according to a fifth embodiment of the present invention.

This embodiment is essentially the same as that illustrated in FIG. 1,except for a part of the double-sided printed board 4 and the insulationresins 5 and 6 shown in FIG. 1. Accordingly, the common parts areindicated with the same symbols as in FIG. 1 to make reference theretowithout any explanation.

In FIG. 5, when conductor patterns, not shown in the drawing, of ametallic printed board 1 and a double-sided printed board 44 are to beconnected with each other, a through hole 47 is formed in the portioncorresponding to the connection of the board 44, a metallic pin 48 isinserted into the through hole, and the pin is fixed to the conductorpattern on the board 44 by soldering.

Then, the board 44 to which the metallic pin 48 is fixed is mounted onthe metallic printed board 1 to solder the electrode pattern, not shownin the drawing but provided on the upper surface of the board 1, withthe lower end of the metallic pin 48. Subsequently, the space betweenboth the boards 1 and 44 is filled with an insulation resin 45, and theresin is cured to fix the boards. Similarly, an insulation resin 46 islaminated on the upper surface of the double-sided printed board 44 andallowed to cure.

In this embodiment, the upper and the lower ends, i.e., the metallicprinted board 1 and the double-sided printed board 44 are supported bythe metallic pin 48, and, at the same timer the conductor patterns oneach of the boards 1 and 44 are soldered together with the metallic pin48 to mechanically stabilize both of the laminated boards. Furthermore,the connection between the circuits provided on both of the boards canbe easily implemented since the conductor patterns provided on each ofthe boards are electrically connected.

This embodiment is also applicable to the first to the fourthembodiments described above.

FIG. 6 is a cross sectional view showing a multilayered metallic printedboard according to a sixth embodiment of the present invention.

This embodiment is essentially the same as that illustrated in FIG. 1,except for the insulation resin 5 shown in FIG. 1. Accordingly, thecommon parts are indicated with the same symbols as in FIG. 1 to makereference thereto without explanation.

In this embodiment, a prepreg 55 is incorporated between the metallicprinted board 1 and the double-sided printed board 4 as shown in thedrawing. That is, a monolithic structure is obtained at the assemblystep by compressing the boards 1 and 4 together with the prepreg 55incorporated therebetween. In this case, a strong and air-tightstructure is obtained by compressing the boards 1 and 4 using a vacuumpress.

This embodiment is also applicable to the first to the fifth embodimentdescribed above.

In case a vacuum press is unapplicable to the process according to thesixth embodiment due to the characteristics of the electronic parts 7 tobe mounted, monolithic molding can be effected by injecting aninsulation resin inside a shaping mold in which a plurality of boardshaving the parts mounted thereon are already set. Also in this case, anair-tight resin portion can be realized while increasing the strength ofthe entire module.

FIG. 7 is a cross sectional view showing a multilayered metallic printedboard according to a seventh embodiment of the present invention.

This embodiment is characterized in a metallic printed board, and theother parts are essentially the same as those illustrated in FIG. 1.Accordingly, the common parts are indicated with the same symbols as inFIG. 1 to make reference thereto without giving any explanation.

In FIG. 7, a metallic printed board 61 is composed of a metallic sheet62 as a base, an insulation layer 63, and a conductor pattern 64provided on the upper surface of the insulation layer 63.

This embodiment is characterized by the metallic printed board 61 whichis formed larger than the double-sided printed board 4 and theinsulation resins 5 and 6 that are formed on the metallic printed board61. In this manner, the conductor pattern 64 on the outer peripheryportions can be exposed to use them as a portion for interconnecting theentire conductor pattern 64 with an external circuit.

By thus exposing the conductor pattern 64 of the metallic printed board61, a more facile operation can be realized in connecting the board withan external circuit.

This embodiment is also applicable to any of the foregoing embodiments,i.e., the first to the sixth embodiments.

FIG. 8 is a cross sectional view showing a multilayered metallic printedboard according to an eighth embodiment of the present invention.

This embodiment is an advanced form of the board according to theseventh embodiment illustrated in FIG. 7.

More specifically, a metallic printed board 71 still larger than thatshown in FIG. 7, is composed of a metallic sheet 72 as a base, aninsulation layer 73, and a conductor pattern 74 provided on the uppersurface of the insulation layer 73. The outer peripheral portion of theboard 71 is bent upward making approximately a right angle with respectto the board, and the edge portion of the bent portion is further foldedmildly downward along an oblique direction.

A mother board 75 is mounted on the conductor pattern 74 provided on theuppermost portion of the folded portion of the metallic printed board 71in such a manner that the mother board may cover the conductor patternfrom the upper side. A conductor pattern 77 formed on the lower side ofthe mother board is connected with the conductor pattern 74 of the board71 by soldering. An insulation layer 76 is provided for the mother board75 as shown in the drawing.

In the manner described in the foregoing, a casing can be established byfolding the outer peripheral portion of the metallic printed board 71upward and further covering the thus formed structure with the motherboard 75 from the upper side. Thus, the circuit of the electronic parts7 mounted inside the casing can be shielded and protected from theoutside.

This embodiment is also applicable to any of the foregoing embodiments,i.e., the first to the sixth embodiments.

FIG. 9 is a cross sectional view showing a molded module comprising amultilayered package and a mother board, according to a ninth embodimentof the present invention. This embodiment is an advanced form of theeighth embodiment illustrated in FIG. 8.

In FIG. 9, more specifically, a metallic printed board 85 which becomesa mother board after mounting the electronic parts, comprises a metallicsheet 88 as a base, an insulation layer 86, and a copper foil 87 of theconductor pattern. The electronic parts 7 are mounted on the uppersurface of the copper foil 87. The parts other than an IC bare chip 7A,such as resistors and capacitors, are referred to hereinafter aselectronic parts.

Aluminum, copper, iron, etc., are used as the metallic sheet 88. Themetallic sheet is provided at a thickness approximately in a range offrom 1 to 3 mm. Suitable materials for the insulation layer 86 includean epoxy resin comprising inorganic fillers of alumina, quartz and thelike, and glass mat, glass non-woven material, non-woven polyamide andthe like being impregnated with an epoxy resin. The thickness of theinsulation layer is approximately in a range of from 0.05 to 0.5 mm.

A multilayered package 80 comprising a plurality of layers of electronicparts therein is disposed over the board 85. A folded metallic printedboard 71A comprises a metallic sheet 72 as a base, which is made ofaluminum, copper, iron or the like. The metallic sheet is preferablyprovided at a thickness approximately in the range of from 0.2 to 1 mmto make the sheet suitable for bending process. However, the thicknessrange is not limited thereto because the thickness can be selectedaccording to the radius of curvature in bending.

The insulation layer 73 to be provided on the inner side of the metallicsheet 72 is preferably made of a flexible material such as polyimide,polyether ether ketone, and aramid, so that it may not be damaged due tobending. The thickness of the insulation layer 73 is approximately inthe range of from 0.02 to 0.4 mm.

The metallic sheet 88 of the metallic board 85 and the metallic sheet 72of the metallic board 71A are made of the same material to set thethermal expansion coefficients of both to the same value. For instance,if copper is used as the metallic sheet 88, the metallic sheet 72 mustbe also made of copper. If aluminum is the material of the metallicsheet the metallic sheet 72 is also made of aluminum. In case a materialhaving a thermal expansion coefficient other than those of copper andaluminum is used, the same material must be used in both the metalsheets 88 and 72 to maintain the thermal expansion coefficient equal inboth sheets.

If a glass epoxy printed board or any printed board other than themetallic printed board is used as the mother board, the material for theprinted board must be such having a thermal expansion coefficient equalto or nearly equal to that of the metallic sheet 72.

A copper foil 74A of the conductor pattern is formed on the innersurface of the insulation layer 73 of the printed board 71A. Anelectrolytic copper foil, a rolled copper foil, or the like is suitablefor use as the copper foil 74A and the copper foil 87 of the board 85,and the copper foils preferably have a thickness of from 1 to 200 μm. Inparticular, the copper foil for use as the copper foil 87 preferably hasa thickness of from 35 to 200 μm, and that for use as the copper foil74A preferably has a thickness of from 5 to 70 μm.

The multilayered package 80 comprises electronic parts 7 which aremounted on the printed board 71A itself, one or more double-sidedprinted boards 4 which are located on the lower side of the drawing, andelectronic parts 7 and IC bare chip 7A which are mounted on the printedboard 4.

The connector pin (metallic pin) 48A mechanically supports the printedboard 4, and connects the electronic parts 7 and IC bare chip 7A mountedon both the surfaces of the printed board 4 with the electronic parts 7mounted on the printed boards 71A and 85 via the copper foils 74A and 87provided as the conductor patterns on the printed boards 71A and 85.

The connector pin 48A is connected previously to the copper foil 74A ofthe printed board 71A by soldering, and the printed board 4 mountedthereon the electronic parts 7 and the like is connected and fixed tothe connector pin 48A by soldering.

As described in the foregoing, the multilayered package 80 includestherein the laminates of printed boards or electronic parts, They arenot necessarily limited to the two-layered structure as shown in thedrawing, but the printed boards 4 can be added to further increase thenumber of the layers.

The IC bare chip 7A undergoes a high speed switching operation, and ismounted on the printed board 4 by wire bonding or bump process. The barechip 7A is generally sealed with a chip coating material such as epoxyresin to protect the chip after mounting.

In general, the IC bare chip 7A undergoes a high speed switchingoperation, and is therefore apt to malfunction due to the crosstalkinside the electronic circuit and to the external noises. Thus, the barechip is preferably mounted indirectly on the printed boards 71A and 85,because they have a large dielectric constant and they therefore tend tocatch noises. Thus, the bare chip is mounted on the printed board 4which is finally sealed with an insulation resin. As a matter of course,the bare chip may be mounted on an already laminated double-sidedprinted board.

The inside of the multilayered package 80 is filled with a highlythermo-conductive insulation resin 81. An epoxy resin containinginorganic fillers of alumina, quartz or the like is used for theinsulation resin 81. The thermal expansion coefficient of the insulationresin must be selected to be a value equal to or nearly equal to that ofthe metallic sheet 72 as the outer frame of the package 80. Forinstance, if copper is used as the metallic sheet 72, an insulationresin having a thermal expansion equal to that of copper is preferablyused. Specifically, a resin having a thermal expansion coefficient atleast in the range of from 15×10⁻⁶ ° C.⁻¹ to 17×10⁻⁶ ° C.⁻¹ is selected.A resin having a thermal expansion coefficient as near as possible tothe value of copper, i.e., 16×10⁻⁶ ° C.⁻¹, is more preferably used. Thethermal expansion coefficient of the entire metallic printed board 71Afalls at a value nearly equal to that of the metallic sheet 72.

By thus setting the thermal expansion coefficient of the insulationresin 81 approximately equal to that of the metallic sheet 72 of thepackage 80, the thermal stress which is applied to the entire module bythe heat generated from the electronic parts 7 and the IC bare chip 7Acan be lowered. In this manner, the peeling off at the boundary betweenthe metallic printed board 71A and the insulation resin 81, or thedisconnection of the copper foil 74A on the board 71A can be preventedfrom occurring.

When aluminum is used for the metallic sheet, an insulation resin 81having the same thermal expansion coefficient as that of aluminum, i.e.,27×10⁻⁶ ° C.⁻¹, is preferably used to fill the inside of the package.The thermal expansion coefficient of the resin must be set at least inthe range of from 26×10⁻⁶ ° C.⁻¹ to 28×10⁻⁶ ° C.⁻¹, and preferably, at avalue as near as possible to 27×10⁻⁶ ° C.⁻¹.

In case a metallic sheet 72 made of a material other than copper oraluminum is used, the use of an insulation resin 81 having a thermalexpansion coefficient matched with that of the metallic sheet 72 isrequired.

The insulation resin 81 is injected into the package under a normalpressure or under a reduced pressure in the range of from 650 to 760Torr. Preferably, the resin is incorporated under a pressure in therange of from 700 to 760 Torr to prevent voids from remaining betweenthe laminated printed boards.

A highly thermally conductive insulation resin 82 is used, after theprinted board 85 as the mother board is jointed to the package 80 bysoldering, for resin-molding the periphery of the solder joint portionsand the entire space defined between the printed board 85 and theinsulation resin 81 inside the package 80.

The insulation resin 82 is made of the same material as the insulationresin 81. Accordingly, the thermal expansion coefficient is the same forboth. Thus, the thermal strain can be reduced in case a thermal stressis applied to the module, and the boundary between the insulation resins81 and 82 can be tightly fixed to prevent peeling off from occurring onthe boundary. Furthermore, the copper foil 74A can be prevented fromsuffering disconnection or damage due to the deformation of the printedboards 71A and 4.

The insulation resin 82 is injected into the package under a normalpressure or under a reduced pressure in the range of from 650 to 760Torr in a manner similar to that employed for the insulation resin 81.Preferably, the resin is incorporated under a pressure in the range offrom 700 to 760 Torr to prevent voids from remaining at a portionadjoining the insulation resin 81 and to effectively discharge thegenerated heat.

Furthermore, the entire periphery inclusive of the space between theprinted board 85 and the package 80 is sealed with an insulation resin82, in order to protect the copper foil 87 and the copper foil 74A inthe vicinity of the joint portion against the external moisture anddust, and to prevent defective connection from occurring due to shortcircuit and deterioration of the foils. Furthermore, the joint portionbetween the printed board 85 and the package 80 is sealed with theinsulation resin 82 to assure the establishment of a tight mechanicaljoint and electric connection between the board and the package. A frame83 for filling the resin is also shown in the drawing.

FIGS. 10(a) and 10(b) are views of a tenth embodiment of the presentinvention, wherein FIG. 10(a) is a cross sectional view of a metallicprinted board 71A for a multilayered packager and FIG. 10(b) is a crosssectional view of a metallic printed board 71B for use similarly as inthe foregoing but with the addition of an insulation sheet to themetallic printed board 71A.

Referring first to FIG. 10(a), the metallic printed board 71A comprisesan insulation layer 73 made of a thermosetting polyimide adhesive sheet,e.g., a polyimide bonding sheet SPB series produced by Nippon SteelCorporation. The use of this particular sheet allows the copper foil 74Aof the conductor pattern to be easily adhered with a metallic sheet 72by using a vacuum heating press and the like.

Referring to FIG. 10(b), the insulation layer 73 is 5 formed on each ofthe copper foil 74A and the metallic sheet 72, and an insulation sheet91 is incorporated between the insulation layers 73 to establish theprinted board 71B.

The insulation sheet 91 is a sheet or a film made of polyimide,polyester, aramid, polyphenylene sulfide, polyether ether ketone, etc.By thus laminating the insulation layer 73 on two layers byincorporating the insulation sheet 91 therebetween, an insulation layerhaving a desired thickness and electric and physical characteristics canbe implemented.

FIGS. 11(a) to 11(e) are views of an eleventh embodiment of the presentinvention, and show steps of producing a multilayered package 80 insequence.

First, FIG. 11(a) is a cross sectional view showing the metallic printedboard 71A for the multilayered package shown in the FIG. 10(a).

FIG. 11(b) is a cross sectional view showing the metallic printed board71A obtained after forming a conductor pattern by etching the copperfoil 74A.

FIG. 11(c) is a plan view showing the punched out metallic printed board71A obtained by pressing after the etching step, so that the structurethus obtained is finally processed into a box-shaped package,

In FIG. 11(c), the four sides which become side walls of the package 80by a subsequent bending process, comprises two side planes (the portionsshown in the right and left sides of the drawing) on which the copperfoil 74A is processed and formed to connect the package with themetallic printed board 85 for the mother board, and two other sideplanes (the portions shown in the upper and lower sides of the drawing)having no copper foil 74A thereon.

In the four sides above, the two side planes having thereon the copperfoil 74A are bent with a radius of curvature in the range of from 1 to 5mm so that the insulation layer 73 may not be damaged. Furthermore,slits 101 are provided on the corner portions of the other two sideplanes having no copper foils 74A thereon at the same radius ofcurvature as that of the bent of the two side planes having the copperfoil, so that the gap at the corner might be minimized when the two sideplanes are butted with the other two side planes having thereon thecopper foils 74A.

The two side planes having no copper foil 74A thereon are bent at anacute angle to minimize the gap and to obtain a deep package when thepunched printed board is shaped into a package.

FIG. 11(d) is a cross sectional view showing a structure which isobtained by mounting electronic parts 7 and a connector pin 48A on thepunched out printed board 71A, which is subjected to pressing and isshown in FIG. 11 (c), and then fixing a double-sided printed board 4already having the electronic parts 7 and IC bare chip 7A to the upperside thereof.

FIG. 11(e) is a cross sectional view showing a structure obtained byfolding the structure shown in FIG. 11(d) into a package structure usinga press. An upper mold 102 and a lower mold 103 both used in the foldingprocess are also shown in the drawing. As a matter of convenience, thedetails in the printed board 71A, such as the metallic sheet 72, theinsulation layer 73, and the copper foil 74A, are not shown individuallyin FIG. 11(e).

The mold 102 referred above has a hollow structure in which the portioncorresponding to the laminate of the printed boards 4 and 71A is bored,so that the printed board 71A can be folded without damaging theelectronic parts 7 and the like mounted on the printed boards 4 and 71A.

Furthermore, the foregoing molds 102 and 103 have the portions on theouter periphery facing to each other being curved at a predeterminedradius of curvature to provide a joint portion with the metallic printedboard 85 of the mother board by curling only the edge portions of thetwo side planes having thereon the copper foil 74A of the board 71A.Although not shown in the drawing, the two molds 102 and 103 are shapedsuch that the two side planes having no copper foil 74A of the board 71Athereon may be bent making an acute angle with a radius of curvature of1 mm or less.

Thus, the multilayered package including multiple layers of electronicparts or printed boards can be obtained by the steps of FIGS. 11(a) to11(e), and the multilayered package 80 is formed by injecting theinsulation resin 81 into the package thus obtained.

If the structure of the molds for folding is changed, the multilayeredpackage with the printed board 71A having a desired depth of side planeand a desired shape, radius of curvature, etc., of the curled portioncan be implemented.

FIGS. 12(a) and 12(b) are views of a twelfth embodiment of the presentinvention.

FIG. 12(a) is a cross sectional view showing the entire structureobtained by solder joining the multilayered package 80 with a metallicprinted board 85. As a matter of convenience, the metallic sheet 72, theinsulation layer 73, the copper foil 74A etc. of the printed board 71Awhich constitutes the package 80 are not shown individually in FIG.12(a).

In FIG. 12(b), an alignment jig 111 is provided for precisely aligningthe package 80 with the printed board 85.

The jig 111 comprises a pin 112. The package 80 can be aligned with theprinted board 85 in a horizontal plane by inserting the pin 112 into apenetration hole provided in the connecting portion (joint portion) ofthe package 80 and in the connecting portion (joint portion) of theprinted board 85. As a matter of courser the penetration holes are boredin portions other than the copper foils 87 and 74A, so the mutualelectric connection between the two copper foils is not impaired.

After aligning the package 80 with the printed board 85 using the pin112, (the tip of) a solder iron 113 is pressed against the curledportion on the lower end of the two sides of the package 80 to fuse thesolder cream previously applied to both the copper foils 87 and 74A. Thecopper foils are connected with each other in this manner. The shape andthe structure of the tip of the solder iron 113 are provided as suchcorresponding to the curled portion to increase the efficiency of heatconduction. Moreover, if the solder iron 113 is used, an already joinedpackage 80 can be easily detached.

The shape of the tip of the solder iron 113 is not necessarily matchedto that of the curled shape, but it may be shaped in accordance with theshape and the structure of the joint portion of the package 80.

In FIGS. 11(a) to 11(e) and 12(a) to 12(b), the metallic printed board71A shown in FIG. 10(a) is used as the multilayered package 80. However,it is also possible to use the metallic printed board 71B shown in FIG.10(b) in the place of the metallic printed board 71A.

As described in the foregoing, the present invention provides thefollowing effects:

According to the first aspect of the present invention, one or moreprinted boards are laminated over a metallic printed board formed of ametallic sheet as a base via an insulation resin. Thus, the mountdensity can be Considerably increased by allowing electronic parts to bemounted on a plurality of layers.

According to the second aspect of the present invention, a resin havinga high thermal conductivity is used as the insulation resin forlamination. Accordingly, a higher mount density can be achieved becausethe heat generated by the mounted parts can be efficiently discharged.

According to the third aspect of the present invention, the insulationlayer is divided into a plurality of portions, and the portions are madeof materials differing from each other in physical properties. Thematerials can be selected according to the operation characteristics ofthe mount circuits, for example, an insulator having a high thermalconductivity or an insulator having a low dielectric constant isselected. As a result, a stable circuit operation can be realized tofurther increase the mount density.

According to the fourth aspect of the present invention, a through holepenetrating the conductor patterns is formed through the laminatedboards. Thus, a connection of the conductor patterns on the boards canbe realized more easily, thereby improving the operability in connectingthe circuits.

According to the fifth aspect of the present invention, a part of theprinted board laminated over the metallic printed board is cut out, anda substrate having thereon a through hole and an electrode pattern forconnection is fitted and buried into the cut-out portion of the printedboard. Thus, the operability in connecting the circuits can be improvedbecause the electrode pattern can be more easily connected with theconductor patterns on other printed boards.

According to the sixth aspect of the present invention, a metallic pinis buried in the thickness direction, which is used to connect theconductor patterns formed on the printed boards facing to each other.Thus, the operability in connecting the circuits can be improved becauseconnection between the conductor patterns on the printed boards becomeseasy.

According to the seventh aspect of the present invention, a multilayeredmetallic printed board is improved in an air-tightness and in strength,because the entire body is obtained by incorporating an insulation resinbetween the printed boards as prepregs and performing the monolithicmolding using a vacuum pump.

According to the eighth aspect of the present invention, a multilayeredmetallic printed board is improved in air-tightness and strength,because a plurality of boards having thereon the mounted parts are setinside a shaping mold and are molded monolithically by injecting aninsulation resin into the mold.

According to the ninth aspect of the present invention, the metallicprinted board larger than the outer periphery of the printed board andthe insulation resin layer formed thereover is formed, and the conductorpattern formed on the surface of the metallic printed board is exposedto form a portion for the connection with an external circuit. Thus, theoperability in the connection with an external circuit can be improvedin this manner.

According to the tenth aspect of the present invention, the edge portionof the metallic printed board is bent upward to form a casing coveringthe printed board portion laminated over the board. Thus, the circuit ofthe mounted parts on the boards can be protected and shielded from theoutside.

According to the eleventh aspect of the present invention, theelectronic parts are mounted on multiple layers including a printedboard as a mother board, a metallic printed board of a multilayered typepackage joined to the mother board by means of soldering and the like,and printed boards inside the multilayered package. Thus, the mountdensity can be considerably increased. At the same time, parts differingin shape can be mounted by taking the spacing of the lamination betweeneach of the printed boards into consideration.

Furthermore, the heat generated from the parts can be allowed to diffuseefficiently via the insulation resin, metallic printed boards, and thelike, and the parts can be protected against external moisture andvarious types of atmospheres to prevent deterioration, by sealing eachof the parts with an insulation resin and by bringing the insulationresin at the package side into close contact with the insulation resinat the metallic printed board side for the mother board. Furthermore,the mechanical strength and the electric reliability of the module canbe improved by assuring a tight integration of the package with themetallic board as the mother board using the insulation resin.

According to the twelfth aspect of the present invention, a metallicsheet is fixed to a copper foil for the conductor pattern with aninsulation layer being incorporated therebetween. Thus, a flexiblemetallic printed board for a multilayered package can be fabricatedeasily, and the operability in bending work can be improved.

According to the thirteenth aspect of the present invention, IC barechips for high speed switching are mounted on the printed board otherthan the metallic printed board inside the multilayered package, andthen the chips are molded with an insulation resin. Thus, a stablecircuit function can be obtained without being influenced by crosstalkand external noises.

According to the fourteenth aspect of the present invention, a deepmultilayered package formed approximately in the shape of a box andhaving substantially no space in the corners can be obtained. Thus, themodule is more suitable for accommodating electronic parts in multiplelayers to achieve high mount density.

According to the fifteenth aspect of the present invention, copper foilsformed on two side planes having a larger radius of curvature are usedfor connection with the printed board as the mother board. Thus, ahighly reliable multilayered package can be obtained free from thedisconnection of copper foil and destruction of the insulation layer.

According to the sixteenth aspect of the present invention, the metallicprinted board alone can be bent and worked without causing damage on theprinted boards and mounted parts inside the multilayered package, and onthe mounted parts on the printed board as the mother board.

According to the seventeenth aspect of the present invention, a reliablemodule can be obtained in which the heat from the parts are effectivelydischarged, and disconnection and the like due to deformation, etc.,attributed to thermal stress is prevented by making the thermalexpansion coefficient of the metallic sheet of the multilayered packageequal to that of the highly thermo-conductive insulation resin.

According to the eighteenth aspect of the present invention, the joiningedge of the multilayered package and that of the printed board as themother board can be accurately aligned in the horizontal direction.Thus, this increases the dimensional precision of the joining position.

According to the nineteenth aspect of the present invention, a solderiron having an iron tip shape corresponding to the joining edge of themultilayered package is used. Thus, the operation of joining ordetaching the package can be effected easily and rapidly.

According to the twentieth aspect of the present invention, as themother board, a printed board having a thermal expansion coefficientequal to or nearly equal to that of the metallic printed board of themultilayered package is used. Thus, the cracks can be prevented fromoccurring on the solder at the joint portion between both the boards,and hence a module improved in mechanical strength and in electricreliability can be implemented.

According to the twenty-first aspect of the present invention, theperipheral portion of the joint between the two printed boards and theportion between the printed board as the mother board and themultilayered portion are filled with a highly thermally conductiveinsulation resin having a thermal expansion coefficient nearly equal tothat of the insulation resin of the package. Thus, the adhesivenessbetween the resins can be improved, and deformation or damage attributedto thermal stress can be prevented to realize a module improved inmechanical strength and in electric reliability.

What is claimed is:
 1. A multilayered printed board structure,comprising:an insulated metal substrate including an insulating layerlaminated on a metallic plate as a base layer and a conductive layer onsaid insulating layer, and having first electronic components mounted onsaid insulated metal substrate; at least one printed board laminatedover a first side of said insulated metal substrate on which said firstelectronic components are mounted, and having second electroniccomponents mounted on one or both sides of said printed board; aninsulating resin filling a space between said insulated metal substrateand said printed board; said printed board or said insulation layer ofsaid insulated metal substrate being divided into at least first andsecond portions, said first portion containing electronic parts similarin first operational characteristics; and said second portion containingparts similar in second operation characteristics, said first and secondoperational characteristics being different; and said portions of saidprinted board or said insulating layer formed of materials differing inphysical properties and selected in relation to the operationalcharacteristics of said electronic parts of said portion.
 2. Amultilayered printed board structure as claimed in claim 1, wherein saidinsulation resin has a high thermal conductivity.
 3. A multilayeredprinted board structure as claimed in claim 1, wherein a through hole isformed in said at least one printed board to penetrate a conductorpattern provided on said at least one printed board.
 4. A multilayeredprinted board structure as claimed in claim 1, further comprising ametallic pin for connecting conductor patterns provided on said boardsfacing to each other, said pin being buried along the thicknessdirection of said multilayered printed board structure.
 5. Amultilayered printed board structure as claimed in claim 1, wherein saidmultilayered printed board structure has a monolithic structure formedby applying a vacuum press to said boards and said insulation resinincorporated as prepregs between each of said boards.
 6. A multilayeredprinted board structure as claimed in claim 1, wherein said multilayeredprinted board structure has a monolithic structure formed by injectingsaid insulation resin into a shaping mold after placing therein said atleast one printed board having said mounted electronic components.
 7. Amultilayered printed board structure as claimed in claim 1, wherein saidinsulated metal substrate is larger than an outer periphery of said atleast one printed board and said insulation resin over said insulatedmetal substrate, and a conductor pattern formed on a surface of saidinsulated metal substrate is exposed to form a connecting portion withan external circuit.
 8. A multilayered printed board structure,comprising:an insulated metal substrate including an insulating layerlaminated on a metallic plate as a base layer and a conductive layer onsaid insulating layer, and having first electronic components mounted onsaid insulated metal substrate; at least one printed board laminatedover a first side of said insulated metal substrate on which said firstelectronic components are mounted, and having second electroniccomponents mounted on one or both sides of said printed board; aninsulation resin filling a space between said insulated metal substrateand said printed board; and wherein said at least one printed boardlaminated over said insulated metal substrate has a cut portion, and asubstrate having thereon a through hole and an electrode pattern beingfitted and buried in said cut portion.
 9. A multilayered printed boardstructure as claimed in claim 8, whereinsaid printed board or saidinsulation layer of said insulated metal substrate is divided into atleast first and second portions, said first portion containingelectronic parts similar in first operational characteristics; and saidsecond portion containing parts similar in second operationcharacteristics, said first and second operational characteristics beingdifferent; and said portions of said printed board or said insulatinglayer formed of materials differing in physical properties and selectedin relation to the operational characteristics of said electronic partsof said portion.
 10. A multilayered printed board structure as claimedin claim 8, wherein said insulation resin has a high thermalconductivity.
 11. A multilayered printed board structure as claimed inclaim 8, including a through hole formed in said at least one printedboard to penetrate a conductor pattern provided on said at least oneprinted board.
 12. A multilayered printed board structure as claimed inclaim 8, further comprising a metallic pin for connecting conductorpatterns provided on said boards facing to each other, said pin beingburied along the thickness direction of said multilayered structureprinted structure.
 13. A multilayered printed board structure as claimedin claim 8, wherein said multilayered printed board structure has amonolithic structure formed by applying a vacuum press to said boardsand said insulation resin incorporated as prepregs between each of saidboards.
 14. A multilayered printed board structure as claimed in claim8, wherein said multilayered printed board structure has a monolithicstructure formed by injecting said insulation resin into a shaping moldafter placing therein said at least one printed board having saidmounted electronic components.
 15. A multilayered printed boardstructure as claimed in claim 8, wherein said insulated metal substrateis larger than an outer periphery of said at least one printed board andsaid insulation resin over said insulated metal substrate, and aconductor pattern formed on a surface of said insulated metal substrateis exposed to form a connecting portion with an external circuit.
 16. Amultilayered printed board structure, comprising:an insulated metalsubstrate including an insulating layer laminated on a metallic plate asa base layer and a conductive layer on said insulating layer, and havingfirst electronic components mounted on said insulated metal substrate;at least one printed board laminated over a first side of said insulatedmetal substrate on which said first electronic components are mounted,and having second electronic components mounted on one or both sides ofsaid printed board; and an insulation resin filling a space between saidinsulated metal substrate and said printed board, an outer edge of saidinsulated metal substrate being folded upward to provide a casing whichsurrounds said at least one printed board laminated over said insulatedmetal substrate.
 17. A multilayered printed board structure as claimedin claim 16, said insulation resin having a high thermal conductivity.18. A multilayered printed board structure as claimed in claim 16,whereinsaid printed board or said insulation layer of said insulatedmetal substrate is divided into at least first and second portions, saidfirst portion containing electronic parts similar in first operationalcharacteristics, and said second portion containing parts similar insecond operation characteristics, said first and second operationalcharacteristics being different; and said portions of said printed boardor said insulating layer formed of materials differing in physicalproperties and selected in relation to the operational characteristicsof said electronic parts of said portion.
 19. A multilayered printedboard structure as claimed in claim 16, wherein a through hole is formedin said at least one printed board to penetrate a conductor patternprovided on said at least one printed board.
 20. A multilayered printedboard structure as claimed in claim 16, said at least one printed boardlaminated over said insulated metal substrate having a cut portion, anda substrate having thereon a through hole and an electrode patternfitted and buried in said cut portion.
 21. A multilayered printed boardstructure as claimed in claim 16, further comprising a metallic pin forconnecting conductor patterns provided on said boards facing to eachother, said pin being burled along the thickness direction of saidmultilayered structure printed structure.
 22. A multilayered printedboard structure as claimed in claim 16, wherein said multilayeredprinted board structure has a monolithic structure formed by applying avacuum press to said boards and said insulation resin incorporated asprepregs between each of said boards.
 23. A multilayered printed boardstructure as claimed in claim 16, wherein said multilayered printedboard structure has a monolithic structure formed by injecting saidinsulation resin into a shaping mold after placing therein said at leastone printed board having said mounted electronic components.
 24. Amultilayered printed board structure as claimed in claim 16, whereinsaid insulated metal substrate is larger than an outer periphery of saidat least one printed board and said insulation resin over said insulatedmetal substrate, and a conductor pattern formed on a surface of saidinsulated metal substrate being exposed to form a connecting portionwith an external circuit.